Photodetectors are indispensable components for most optoelectronic applications due to their ability to convert light signals into electrical signals. Compared with the renowned III-V compound-based photodetectors, silicon (Si)-based photodetectors can be easily integrated with the conventional Si-based complementary-metal-oxide-semiconductor (CMOS) technology. Although conventional p-n and p-i-n photodiodes are popular device structures, they suffer from low responsivity and quantum efficiency. Therefore, it is necessary to boost their electrical signals to an acceptable range via amplifiers.
Metal-oxide-semiconductor field-effect-transistors (MOSFETs) exhibit exceptional photo sensing capability. MOSFET type photodetectors, also known as phototransistors, have the advantages of not only high photo sensitivity and responsivity, but also integrability into conventional CMOS chips. However, some shortcomings still exist due to structural limitations, such as limited light-sensing area and light blocking by gate electrodes. More importantly, these devices are built on rigid substrates, making it difficult to manipulate the physical shapes of the photodetectors.